1. Field of the Invention
This invention relates broadly to couplings and more specifically to couplings for providing a substantially soil tight joint between abutting ends of helically corrugated spiral pipe.
2. Prior Art
In general, most applications of helically corrugated spiral pipe require that the pipe be soil tight and convey liquids, such as water, without gross leakage, as this would cause undue setting or erosion of the soil surrounding the pipe. Furthermore, the pipe joints must also provide sufficient strength to maintain the proper alignment of the joined pipe sections throughout the life of the pipe. In joining adjacent sections of helically corrugated, spiral pipe, the prior art has found that the corrugations of the pipe sections to be joined and the corrugations of band-type couplings must be of substantially the same pitch, size and depth. Good examples of this earlier art can be found in: Campbell, U.S. Pat. No. 3,239,254 issued Mar. 8, 1966 and entitled "Pipe Coupling" and Wiley, U.S. Pat. No. 3,298,721 issued Jan. 17, 1967 and entitled "Coupling Band for Joining Corrugated Pipes". However, the use of these coupling devices required that the corrugations of the abutting pipes be aligned so that the band can properly seat on the pipe section ends. This generally requires rotation of one pipe which is very time consuming and not practical particularly in large diameter pipes. This and other problems, as more completely discussed in Boynton et al. U.S. Pat. No. 3,501,179 issued Mar. 17, 1970, and entitled "Helically Corrugated Spiral Pipe and Coupling Therefor", have led to attempts to rectify these problems. One of the earlier attempts and one most closely related to this invention is disclosed in Davis U.S. Pat. No. 3,315,991 issued Apr. 25, 1967 and entitled "Pipe Coupling" and is also discussed in the aforementioned Boynton et al. U.S. Pat. No. 3,501,179. In this disclosure, a pair of narrow, deformable elongated strips having a broad base are strapped to each pipe by a special metal band which upon tightening deforms the strips to match the pipe corrugations. The difficulty in such a design is the ability of the deformed narrow strips to form and maintain the necessary seal particularly in pipes having corrugations with great depth, and in cases where settling of the pipes is likely to occur. For this reason, the most commonly used corrugated pipe, particularly where proper seals are necessary is reformed pipe wherein the helical corrugations at the pipe ends have been reworked into annular corrugations. This pipe design is much easier to seal with various couplings such as that shown in the aforementioned Boynton et al. U.S. Pat. No. 3,501,179. The effectiveness of this arrangement, as attested by its wide industry usage, however, relies on a re-worked pipe whose costs is substantially higher than the helically corrugated spiral pipe. Therefore, if a coupling providing adequate sealing and which could be used on the helically corrugated spiral pipe is available substantial time, equipment and money savings could be realized.